In the study of the human filariases, progress has been hampered by: 1) the lack of defined parasite antigens; 2) the broad immunological cross-reactivity seen among the eight filarial species of humans; and 3) the dearth of abundant parasite material. The objectives of this project are to define and generate filarial proteins that are important in including parasite-specific immune response in the human host and to understand, at a molecular level, the differences among related filarial species. cDNA and genomic libraries have been either constructed (Brugia malayi and Wuchereria bancrofti) or made available (Onchocerca volvulus) so that screening with defined patient sera or patient T cells could be performed. Recombinant antigens and probes have been identified that: a) induce T cell responses in an antigen- specific manner; b) may be in part protective in onchocerciasis; c) can distinguish among related filarial species by restriction fragment length polymorphisms; d) encode for an immunodominant molecular in W. bancrofti; and e) identify a tandemly repeated segment of the W. bancrofti genome.